At the time, Mandel was running for U.S. Senate against incumbent Democratic U.S. Sen. Sherrod Brown. Mandel sent a strongly worded two-page letter on state letterhead to California Treasurer Bill Lockyer in May 2011. Just days later, $100,000 in contributions poured into Mandel's Senate campaign from Suarez employees.

In a separate letter to U.S. Rep. Jim Renacci, R-Wadsworth, on March 21, 2011, Mandel urged the congressman to sponsor a bill that would head off such lawsuits.

Federal authorities allege that Suarez and his chief financial officer, Michael Giorgio, illegally lined up conduits to donate the money and then tried to cover up the scheme. In September, Suarez and Giorgio pleaded not guilty to federal charges of campaign finance violations, obstruction of justice and witness tampering.

It is illegal to give campaign money in the name of another individual, and federal campaign law currently limits individual candidate contributions to $2,600. Mandel, who lost the Senate race, has not been accused of any wrongdoing.

Mandel is running for re-election as state treasurer. His challenger is state Rep. Connie Pillich, D-Cincinnati.

The criminal case against Suarez and Giorgio is scheduled to go to trial in June in front of U.S. District Court Judge Patricia Gaughan.